Relay setup to ensure power failure

[wayne.workman2012]

Hello,

This is my first post here - hoping to get some help with a unique project. I'm somewhat familiar with very basic circuitry but I need some help with this one.

Firstly - I'm active in the open source programming community. The other day I came across a project called PirateBox. It interestes me greatly. This project promotes the 1st amendment of the U.S. constitution and is also protected by the 4th amendment. Here is the project's website: http://piratebox.cc/ and a short video about it here:
https://www.youtube.com/watch?v=WEGgUw34F1E

The project is already available via the Google Play store, and has been ported to iOS and Windows Mobile (because it's open source).
https://play.google.com/store/apps/details?id=de.fun2code.android.piratebox&hl=en



I plan to adapt the storage of this project in a way that it becomes volatile - meaning that power loss causes loss of the shared storage - and I also plan to modify the project so that shared files have a limited lifespan (1 hour). These things I don't need help with setting up. Instead of using a Raspberry Pi or a flash-able consumer grade router as is common with the project, I plan to run it on a full ATX motherboard that has a 12v input built onboard, and I plan to host this setup 24/7 in my car.

So, I've been researching a lot. I've figured out that I need a secondary battery, and a four-post solenoid battery isolator. The power loss functionality should be activated when a door or hatch is opened, or if the motor starting battery looses connection.

I have figured that I can probably use one Normally Open relay and one Normally Closed relay to achieve this.

I believe I can wire the normally closed relay in parallel with my vehicle's dome light, and wire the normally open relay in series with the normally closed relay to the car starting battery. This way - if a door or hatch becomes ajar - the normally closed relay will open, and if the main battery of the vehicle is disconnected, the normally open relay will open - thus causing a powerloss to the Pirate Box - while the main load of the Pirate Box is carried by the secondary battery - which I'd like to use a sealed 65ah solar battery for.

Although I'm afraid that the high cranking amp requirements of the engine might damage the battery - I'm unsure on this. I'd rather not use an unsealed lead acid battery due to the fumes it produces when charging

I've ordered a 12v 20amp normally open relay and a 12v 20amp normally closed relay already - going to play around with those and two small 12v batteries when they come in. However any insight into how to wire this would be greatly appreciated.

Thanks,
Wayne

[Seabottom]

This sounds rather straight forward, if we're just talking about if you need to detect whether or not a few switches have been activated.

What exactly is it that you need to power with 20 amps?

Basically, all you want is just one relay that detects if any doors or hatches have been opened or if the lights are on. Your car already has sensors that detects if anythings open in the car, but I reckon that those would be connected via low voltage directly to the computer.

this means you would have to install physical switches in series with each other, one end goes to the car battery, the other end of the switch string goes to the relay. Note that all of your switches should be NC for this to work.
It's really simply so if one of your switches have been activated the power to realy disappears and whatever it was powering before hand is now powerless which is what you want right?

There's no need for a secondary battery unless the thing you're trying to power takes more power from the car than the generator can recharge. There's no fun in having a car that won't start am I right?
If you chose to have a second battery there is no need to involve the main battery and so there would be no interference on either of those circuits. You do have to connect ground on Battery #2 to the ground on Bettery #1 though - usually this is easily done by attaching a lead to anywhere on the chassis with good contact.